Gaseous conduction device



July 28, 1931. c. G. SMITH GASEOUS CONDUCTION DEVICE Filed Dec. 21, 1925 ,Zeu

Patented July 1931 UNITED STATES PATENT OFFICE CHARLES G. SMITH, OF MEDFOBD, MASSACHUSETTS, ASSIGNOR TO BAYTHEON CAMBRIDGE, MASSACHUSETTS, A CORPORATION OF MASSACHUSETTS me, or

Gaseous connoo'rron DEVICE Application Med December 21, 1825. Serial No. 78,794.

This invention relates to electronic dis- I charge tubes generally but more particularly to gaseous discharge tubes in contradistinction to thermionic tubes, and may be used 'g' n conjunction with the inventions claimed in certain applications Serial Nos. 526,095, now Patent 1,617,179, granted February 8,

Principal objects of the invention are to increase the magnitude of discharge and to 16* In gaseous discharge tubes the voltage drop between cathode and anode, when substantial discharge is taking place, is comparative- 1y high, being in many cases somewhat greater than the ionizatlon or resonance voltage of the gas. According to thisinvention the voltage drop may be decreased far below the ionization voltage and without heating the cathode to excessive temperature. This is effected by intensely ionizing the gas 26 over a large area of cathode surface by a current produced by an electromotive force which is independent of the voltage drop between cathode and anode.

The genus of the invention is set forth in the appended claims and illustrated 1n the accompanying drawings in whlch Fig. 1 is a vertical longitudlnal sectlon-of one embodiment; Fig. 2 is a section on line 2-2 of Fig. 1;

Fig. 3 is a section on line 3-3 of 'Fig. 1; Fig. 4 is a vertical longitudinal sectlon of another embodiment;

Fig. 5 is asection on line 55 of Fig. 4; Fig. 6 is a vertical longitudinal section of another embodiment; and

Fig. 7 is still another form of the invention. The particular embodiment illustrated in Figs. 1, 2 and 3 comprises a tube '1 containing a cathode in the form of a toroid WhlCl] is divided on one side to form a gap 3 between the two ends 4 and 5. At a point opposite thegap 3 a tube 6 communicates with the interior of the cathode, the tube depending to a point below the 'surface of a pool of; mercury 7 in the lower end of the contamer so t at the mercury rises into the tube 6, for the purpose of heat insulation. A cylinder of insulation 8 may be provided around the lower end of the tube 6. The cathode may be mounted in the container or housing 1 in any suitable manner as for example on the lead 40. A cylinder 9 of magnetic material is mounted around the tube 6 somewhat above the level of the mercury 7, this cylinder being heated sufiiciently to vaporize the mercury in the tube 6 by current induced therein as hereinafter described. The anode is in the form of a plate 10 disposed in a planev passing through the gap 3. A magnetic coil I 11 surrounds the tube preferably in the horizontal plane of the toroidal .cathode, for the purpose of producing induction currents in the gas within the cathode and also in the cylinder 9, as hereinafter described. The gas within the tube is preferably mercury va or at a pressure of the order of .Olmm. alt ough different gases may be employed either singly or in mixture.

By passlng current of high frequency (for example 10 cycles per see.) through coil 11, induced current is caused to flow around the toroid in the gas contained within the toroid, eddy currents in the toroid itself being restricted by the gap 3. With an induced current of sufiicient ma itude the gas within the toroid and across't e gap 3 may be ionized intensely. For this purpose the current in coil 11 preferably has an electromotive force per turn of more than the ionization volta of the gas (or vapor) within the toroid. T e induced current 1n the gasv within the toroid should be uite large and for most purposesshoul be several amperes. This current furnishes a cgpious supply of ions in- .to start the discharge.

From the foregoing it will be evident that the low voltage .drop between cathode and anode results from the intense ionization produced inside the hollow cathode and across the gap 3 b the high frequency current which is independent of the voltage drop between'cathodeand anode. The discharge between the cathode and anode is spread out over a large area inside the hollow cathode and consequently local heating of the cathode, which often leads to its destruction, is avoided. Moreover, the total losses in the tube are much lower than in the ordinary tube. Furthermore the very low voltage drop between cathode and anode throughout the range of operation of the tube permits the device, when used as a rectifier, to be operated in parallel with similar tubes without employing series reactancesto effect a proper division of load, or at least only small reactances, owing to the fact that this tube has a rising current-voltage characteristic.

The form of the inventionillustrate'd in Figs. 4 and 5 comprises a hollow cathode 12 in the form of a cup having a discharge opening 13 in its lower end and having its upper end open. The anode 14 is located in the bottom of the tube and the opposing surfaces of the two electrodes are preferably placed sufficiently close toeach other (for example inch apart) to prevent substantial ionization in the gap therebetweenas a result of electrons passing directly across the space. it being understood that the discharge passes between the interior of the hollowcathode within the hollow cathode upon the lead 16 and current is induced in this ring by high frequency current in the coil 16 which is coaxial with the ring and the cathode.

The cathode is preferably slit at intervals as illustrated at 17 to restrict eddy currents therein and the cathode is preferably formed of nonmagnetic material so as not to shield the ring 15. The cathode preferably fits within the glass tube with a very small clearance and may be mounted in any suitable way, as for example, upon leads 18. In this form of tube the gas is preferably inert monatoniic gas such as argon, neon or helium.

The tube illustrated in Figs. 4 and 5' is referably operated as follows: The ring 15 is heated with eddy currents induced by coil 16 to a sufiicient temperature to emit electrons for starting purposes and inasmuch as its primary function is for starting the main discharge between cathode and anode, it is preferably connected to the source of. current through a resistance 19 so that only a small amount of current can pass between it and the anode after the tube is in operation. The ring 15 is made sufficiently small so that eddy currents are produced in the gas within the hollow cathode as well as in the body of the ring, whereby the gas adjacent the inner surface of the cathode may be ionized intensely with the attendant advantages described in connection with the first embodi ment. Indeed in this form the entire interior of the cathode is ionized by the eddy currents induced therein by the high frequency cur-- rent in coil 16.

The embodiment illustrated in Fig. 6 comprises a hollow cathode 21 having a discharge opening-22 in its upper end and having at its lower end a tube 23 depending into a pool of mercury 2-1. The anodes 25 and 26 are presented to the interior of the hollow cathode through the opcning 22. Surrounding the cathode is a cylindrical shield 27 which is mountedon the tube 23 at 28 and has an opening in the path of the discharge between the interior of the cathode and anodes. 29 indicates the high frequency coil such as above described. In. this form the cathode is made of a suitable conducting material and the shield 27 is non-magnetic and vertically slotted at intervals so that eddy currents may be induced in the cathode to heat it to incandescence. The shield 27 serves to restrict the radiation of heat from the cathode thereby to maintain the cathode at incandescence with less loss by radiation.

In operating a tube such as illustrated in Fig. 6 the high temperature of the cathode partially ionizes the vapor inside the cathode thereby rendering the gas conducting. The high frequency coil 29 can then more readily induce eddy currents in the gas within the cathode thereby heating the gas still hotter and increasing the state of ionization. Consequently in this case the voltage drop per electron mean free path in the eddy currents does not need to be as high as the ionization voltage. It will be understood that this double anode construction may be used for various purposes such as full rectification of alternating current, in which case the dis-' charge passes" alternately between the anodes and the interior of the cathode. Obviously two anodes could be employed in either of the other embodiments herein disclosed.

The tubeillustrated in Fig. 7 comprises a plate anode 31 and a cathode in the form of a coiled conductor having one turn 32 in the lower end of the tube and one or more turns 33 in the region of the anode, the ends of the upper and lower turns being connected at 34 and 35 to form anendless conductor. The high frequency magnetic coil 36 surrounds the tube in the region of the lower turn of the cathode and induces current in said cathode and induces current in said lower turn. This induced current flows through the connecting portions 34 and 35, and thence through the upper turn 33, the current in mounted on the upper turn in radial planes to obstruct eddy currents in the gas around the upper turn 33 in order to localize the eddy currents in the gas within the upper turn. A shield 38, preferably though not necessarily of insulating material, may also be arranged to extend diametrically across the lower end of the tube to obstruct eddy currents in the gas in'the region of the lower turn 32. The cathode may be supported in its axis extending through the region of the source of electronic discharge (in the region of the cathode), the coil constituting induction means for inducing current in a closed orbit in the region of the source of discharge. While the induced currents are referably in the gas, adjacent the acting sur ace of the cathode, they may be induced in a metallic ring or cylinder as illustrated in Figs. 4, 5, 6 and 7. I

I claim:

1. A gaseous discharge device comprising a sealed container, ahollow cathode having a restricted discharge opening and adapted to emit electrons from its interior surface, an. anode in spaced relation to said cathode,

an auxiliary cathode within said hollow.

cathode and connected to said hollow cathode, means for inducing eddy currents in said auxiliary cathode, and means for prevgnting eddy currents in said hollow catho e.

voltage for producing a discharge along said paths and ionizing the gas therein to provide electric carriers for maintaining a discharge between said cathode and said anode. Signed by me at Boston, 'Massachusetts, this tenth day of December, 1925.

CHARLES G; SMITH.

. 2. A space current device comprising anj envelope containing a gas, a cathode and an anode spaced from each other within said envelope, means adjacent said cathode enclosing, adjacent the surface of the cathode, a body of gas constituting paths for inducing therein voltages adapted to roducea discharge along said paths in sai gas, and high frequency inducing means for inducing 1n said gas paths a voltage to produce a discharge in said paths forionizing the enclosed gas to provide electric carriers for maintaining a discharge between said cathode and said anode. r i

3. A space current device comprising an .envelope cqntaining a gas, an anode-in said 

